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|United States Patent
August 18, 1992
Plastic sheets for use in agriculture
The invention relates to polymeric mulch sheets and mulch films for use in
agriculture. These filter out a large part of the solar radiation which
promotes photosynthesis and plant development, and transmits enough solar
radiation so as to heat the soil beneath such films. The sheets or films
have a green color and transmit about 15-30 percent of the energy in the
green range, and a large percentage of the energy in the 730 to 1100 nm
range. Such mulch films substantially reduce weed growth. The invention
further relates to a method of plant cultivation where the plants are
cultivated, using sheets or films according to the invention.
Foreign Application Priority Data
Allingham; Yael (P.O. Box 14, Benjamina, IL)
May 9, 1990|
|Current U.S. Class:
||47/9; 47/DIG.6 |
|Field of Search:
47/9 S,DIG. 6
U.S. Patent Documents
|Foreign Patent Documents|
Primary Examiner: Raduazo; Henry E.
Attorney, Agent or Firm: Schindler; Edwin D.
1. A polymeric mulch film or sheet for use in agriculture comprising a
green color which filters out over 90% of the photosynthetic active
radiation for photosynthesis and for plant development, said
photosynthetic active radiation filtered out being in the red range and
blue range of the electromagnetic spectum, said polymeric mulch film or
sheet transmitting about 15-40% solar energy in the green range with a
maximum transmittance being obtained at approximately 560 nm, said
polymeric mulch film or sheet further transmitting in the far red range at
approximately 750-1,100 nm.
2. A film or sheet according to claim 1, which transmits about 20 percent
of the solar radiation in the green color range.
3. A film according to claim 1, which contains a stabilizer against
UV-radiation degradation, and which is about 20 to 100 microns thick.
4. A film according to claim 1, made of low density polyethylene, of linear
low density polyethylene, of PVC, or of vinyl acetate polyethylene
5. A film according to claim 1, which transmits enough solar energy to heat
the soil beneath the mulch film, so as to promote plant growth and prevent
infestation with weeds.
FIELD OF THE INVENTION
The invention relates to mulch film for use in agriculture. The film is
opaque to the photosynthetic active radiation (PAR) required for plant
development which encourages weed growth. However, it transmits solar
radiation in the Far-red and some of the green part of the spectrum thus
heating the soil covered by the mulch. This mulch will allow roots of
crops grown under it to have no weeds to compete with, without the use of
herbicides and higher temperature than under black film for root
BACKTROUND OF THE INVENTION
Polyethylene (PE) is a favoured plastic as film in the use of agriculture
for its cheapness, flexibility, and ease to manufacture. It can be had in
a variety of thicknesses and width. It is known in its low density form
(LDPE) and recently as linear low density (LLDPE). The latter has
preferred mechanical strength and can be used as a 20 micron film, for
mulching. Both PE films can be stabilizied against UV radiation by the use
of Hindered Amines Light Stabilizers (HALS) with the addiion of
hydroxy-benzophenones. The sun's radiation reaching the earth's surface
consists of about 53% light intensity in the visible part of the spectrum,
0.4.0.7 microns which is also PAR with a maximum intensity at 0.56
mcirons, the green light being at about 0.56.mu., 3% in the ultra violet
(UV), from 0.3-0.4 microns; and 40% in the far red (FR) from 0.7-1.1
mcirons. Roots of agricultural crops sown or planted out in Spring or
Summer have to be protected from loss of water by evaporation from the
surface of the soil. Cooling of the soil is caused by evaporation,
radiation at night and heat conductivity.
Evaporation and temperature can be controlled by a plastic film cover
termed "mulch". Furthermore, young crop seedlings should not have to
compete with weeds for water and nutriments; this can be achieved by use
of herbicides, elimination of light, or as we claims by elimination of the
Photosynthetic Active Radiation.
The practice is to spread plastic sheets on the surface of the soil, make
holes at intervals to sow seeds or plant crop seedlings. Using black PE
mulch which does not transmit the sun's radiation prevents the growth of
weeds and stops evaporation but it does not heat the soil as it does not
transmit any radiation. The plastic itself warms up and can cause severe
scorching of young seedlings that touch it. Clear PE film which transmits
all the solar radiation will heat up the soil but will also encourage the
growth of weeds unless a herbicide has been applied.
We are aware of commercial films claiming the reduction of transmission of
solar radiation and thus preventing weed formation. U.S. Pat. No.
3,857,807 (Montecatini) claims that PVC films which selectively allow
transmission of visible light and FR increase crop yield compared to black
film mulch. Surprisingly, they allow the transmission of red light 0.6-0.7
microns which is PAR that encourages wee dgrowth. They may have used
herbicides. They further claim they allow 60-90% transmission of radiation
above 0.1 micron which is surprising as there is no radiation below 0.3
microns reaching the earth's surface.
SUMMARY OF THE INVENTION
According to the present invention there are provided novel, improved mulch
films. These are photosensitive and are characterized in that they
transmit energy in the green color range of the spectrum, and also some of
the far red. According to a preferred embodiment of the vention there are
used mulch films which transmit from about 15 to about 40 percent of the
total solar energy in the green range, the preferred transmission being
about 20 percent of this energy in the green, with a maximum at about 0.56
Furthermore the films transmit in the far red, from about 0.75.mu. and up.
The films of the invention are produced from a suitable polymer into which
there is incorporated a predetermined quantity of a pigment which imparts
to it a green color, preferably in conjunction with a UV absorber.
According to a preferred embodiment PE films are used, and pigment is added
so as to allow the passage of about 20 percent of the solar energy in the
Such films are of any desired thickness, the preferred range being about 20
microns to about 75 microns thickness.
Preferably linear low density polyethylene (LLDPE) is used. There can also
be used a PVC sheet, a vinyl acetate polyethylene copolymer (EVA) as well
as other commercially available polymers having similar properties.
UV absorber is used to prevent degradation by solar energy. There are used
commercially available UV absorbers, according to the instructions of the
Preferably organic pigments are used, the quantity used being such as to
result in the desired percentage of transmission in the green, which is
generally about 5 to 10 weight percent calculated on the weight of the
Such novel mulch films can be used in the open field, in tunnels (walk-in
and low ones) as well as in greenhouses.
The mulch film is spread out on the soil before sowing and before planting
of seedlings, which is dones through holes made in the film at required
distances from each other. Such films remain in place for the entire
duration of the cultivation.
Comparisons were made between transparent polyethylene sheeting, black
commercial mulch film and mulch films of the present invention
transmitting various percentages of the green radiation. There was also
used for comparison an aluminized film transmitting a certain percentage
(about 50 percent) of the entire range of solar spectrum.
In the following results are presented which demonstrate that the best
results are obtained with mulch films of the invention, of green color,
and which transmit preferably about 20 percent of the total energy in the
The most efficient mulch was the one that absorbed all the PAR except for
about 20% of the green, with a peak at 0.56 microns and transmitted in
addition, all the Far Red thus preventing weed growth and warming the soil
to within the temperature reached by clear PE. The films used in the
trials were always of a thickness essentially between 20-80 microns'
85 Kg. LLDPE (Linear Low Density PE) Dowlex of Dow Chemical Co., were
stabilized with Chimassorb 944 and Chimassorb 81 (Ciba Geigy) as
recommended by the manufacturer. This was mixed in an extruder with master
batches (concentration of 40% pigment in LDPE) of Hoechst pigments 45 kg
blue BNAE and 4 kg red BBCE and 7 kg yellow GGAE, and blown into a sleeve
of 1.5 meter circumference and of 30 micron thickness. The sleeve was slit
lengthwise to give a flat film. This film did not transmit any visible
light but only the FR.
62 kg LDPE 31 kg LLDPE stabilized as in Example 1, were mixed with
master-batch of Hoechst's 3 kg blue BNAE and 3 kg yellow HRAE in an
extruder as in Example 1. The film transmitted 40% of the green at 0.56
microns and all the far-red.
62 LDPE, 3%/kg LLDPE stabilized as in Example 1, and 6 kg of master batch
Vis-Col of CONSTAB CO. were made into a film as above (green color). The
film transmitted 20% of green at 0.56 micron and all FR.
Methods and Trials
Weed control trials were performed in a light loamy soil. A drip irrigation
system was laid in the center of each plot, four rows of seeds of common
weeds were sown, each plot was covered with one of the test films; one
remaining plot was not covered, as control.
At the end of 4 weeks, a good growth of weeds covered the control plot and
the one under clear PE. An appreciable growth developed under the
aluminized film and under Example 2. Under films of Examples 1, 3 and
black mulch, a few seeds germinated but were etiolated, and did not
Heat Content of the Soil
The temperatures were recorded with the aid of sensors inserted into the
soil at surface 3, 9 and 27 cm depth, and recorded over 24 hour periods.
Highest temperature was recorded under clear PE and lowest under black PE.
The green mulch reached temperatures near those of PE.
a) Melons grown under mulch of Example 3, ripened a week earlier than those
under black film.
b) Gypsophyla flower psikes were ready for cutting earlier than under black
The green photo selective mulch, Example 3, has an advantage over black and
clear mulch film as it prevents weed growth without the use of herbicides
and warms the soil up almost as clear PE.
Results obtained in all the experiments indicate a substantial reduction of
the incidence of weed growth, and this without the use of any herbicide.
(Comparative experiments with transparent PE film show that there occurred
a heavy growth of weeds, preventing development of the seedlings.)
With black mulch film weed growth was inhibited, but the temperature of the
soil was lower than under the green mulch film, and as a consequence crops
(vegetables and flowers) developed later than under the green film. This
earlier ripening, for example of melons, tomatoes, flowers etc. is of
great commercial significance, as the earlier crops can be sold at
considerably higher prices.
The elimination fo the requirement to use herbicides is of crucial
importance especially as regards residual toxicity, not to mention the
high cost of such herbicides.
The conclusions are as follows:
AT the end of 4 weeks, a heavy growth of weeds was observed in the control
plot and under clear PE mulch.
Weed growth clear PE was so vigorous that it lifted the mulch film. Under
aluminized mulch an appreciable growth of weeds was observed.
Under Example 2 which transmitted 40% of green lights, some weeks
developed. Under green mulch film of the invention, Example 3, and under
black mulch, a few seed germinated, but growth was poor and plants were
etiolated with little chlorphyl.
The temperature in the soil under clear PE and mulch films was recorded.
The number of hours at different temperatures below 20.degree. C. was
The hour-degree below 20.degree. C. gives the energy content difference in
soil under the mulches.
Lower number of hours below 20.degree. C. highest under PE with green film
of the invention, was appreciably close to it as well as that in Examples
1 and 2.
Under aluminized mulch and black mulch, more hours under 20.degree. C. were
recorded, indicating lower temperatures and lower heat content in soil.
As mulch film under Examples 1 and 2 showed poor weed control, mulch of the
invention indicated both weed control and more heat-content in soil.